I had the same idea with you to train him as PF but an other experienced person (he is in Nt team) said me to train him first outside skills until 21...My point is to get as much money as i can when i will sell him so his idea sounds attractive
Both ideas for this player is right...depends on in which position you want him to be more useful and in which categories..
This player can be perfect for a PF,you can train his OD first to 8,then IS and later ID.
When that is done just train rebounds/ some JS and you will have a multiskilled PF.
SF will take way too long and he is almost 20/ and his height,you need 13/14 OD and 11/12 ID.
To train a SF ,you need a trainee who has a complete skillset,because training a SF is a very long road..